Aircraft modal suppression system

This disclosure relates to systems and methods for aircraft control. More specifically, the disclosed embodiments relate to aircraft modal suppression.

Known solutions for designing modal suppression control laws are based on turbulence models which rely on uniform gusts and fail to capture the non-uniform contributions of gusts found in nature. This deficiency limits the performance of the previous modal suppression functions, and in some cases may limit its benefit completely. Without an accurate gust input model, the response of the airframe in turbulence remains a challenging problem in modal suppression. Only a model which accurately captures the effect of gust penetration can provide an appropriate foundation to design a feedback control system. Accordingly, improvements are required in the field of aircraft modal suppression.

The present disclosure provides systems, apparatuses, and methods relating to aircraft modal suppression.

The presently disclosed methods include, for example, a method of aircraft modal suppression that includes receiving a plurality of signals from on-board inertial sensors of an aircraft, the plurality of signals corresponding to motions of one or more portions of the aircraft; utilizing the plurality of signals to generate a plurality of observers, each observer comprising one or more estimated states of the aircraft; utilizing the observers to determine control law commands for controlling one or more control surfaces of the aircraft, wherein the control law commands are configured to reduce vibration of the aircraft that is induced by a combination of lateral wind gusts (which may be uniform or non-uniform) and non-uniform vertical wind gusts; and moving the one or more control surfaces of the aircraft in accordance with the control law commands.

In some methods according to the present teachings, the plurality of sensor signals may include a first lateral acceleration at a forward portion of a fuselage of the aircraft; a second lateral acceleration at an aft portion of the fuselage of the aircraft; a third lateral acceleration at a midportion of the fuselage of the aircraft; a yaw rate at the midportion of the fuselage of the aircraft; and a roll rate at the midportion of the fuselage of the aircraft.

In some methods according to the present teachings, each observer may include one or more estimated states of a respective one of the control surfaces. In some cases, the control surfaces may include a rudder of the aircraft; ailerons of the aircraft; and/or flaperons of the aircraft.

In some methods according to the present teachings, the control law commands for the ailerons and/or the flaperons of the aircraft may be antisymmetric.

In some methods according to the present teachings, the control law commands may be configured to dampen lateral mode excitations, and in some cases, elastic contributions to the lateral mode excitations contain frequency components below 10 Hertz.

In some methods according to the present teachings, generating the plurality of observers includes applying one or more operations to one or more of the plurality of signals, the operations including at least one of addition, subtraction, and filtering.

The present teachings further describe a data processing system for aircraft modal suppression, including one or more processors; a memory; and a plurality of instructions stored in the memory and executable by the one or more processors to receive a plurality of signals from on-board inertial sensors of an aircraft, the plurality of signals corresponding to motions of one or more portions of the aircraft; utilize the plurality of signals to generate a plurality of observers, each observer comprising one or more estimated states of the aircraft; utilize the observers to determine control law commands for one or more control surfaces of the aircraft, wherein the control law commands are configured to reduce vibration of the aircraft that is induced by a combination of uniform or non-uniform lateral wind gusts and non-uniform vertical wind gusts; and control the one or more control surfaces of the aircraft in accordance with the control law commands.

In some systems according to the present teachings, the plurality of signals received by the one or more processors includes a first lateral acceleration at a forward portion of a fuselage of the aircraft; a second lateral acceleration at an aft portion of the fuselage of the aircraft; a third lateral acceleration at a midportion of the fuselage of the aircraft; a yaw rate at the midportion of the fuselage of the aircraft; and a roll rate at the midportion of the fuselage of the aircraft.

In some systems according to the present teachings, each observer comprises one or more estimated states of a respective one of the control surfaces. In some systems, the control surfaces include a rudder of the aircraft; ailerons of the aircraft; and/or flaperons of the aircraft.

In some systems according to the present teachings, the control law commands for the ailerons and/or the flaperons of the aircraft are antisymmetric.

In some systems according to the present teachings, the control law commands are configured to dampen lateral mode excitations. In some systems, the lateral mode excitations have frequencies less than 10 Hertz.

In some systems according to the present teachings, generating the plurality of observers includes applying one or more operations to one or more of the plurality of signals, the operations including at least one of addition, subtraction, and filtering.

The present teachings also disclose methods of reducing aircraft vibrations induced by wind gusts, including measuring motions of the aircraft including at least one lateral acceleration, a roll rate, and a yaw rate; using the measured motions of the aircraft to estimate vibrations along the body of the aircraft induced by a combination of uniform or non-uniform lateral wind gusts and non-uniform vertical wind gusts; and compensating for the estimated vibrations by moving at least one of the aircraft ailerons and the aircraft flaperons.

In some methods according to the present teachings, measuring the motions of the aircraft includes measuring lateral accelerations of a nose portion, a tail portion and a center of gravity portion of the aircraft, and measuring a roll rate and a yaw rate of the center of gravity portion of the aircraft; and compensating for the estimated vibrations includes compensating for estimated lateral mode excitations having elastic mode frequencies less than 10 Hertz.

Features, functions, and advantages may be achieved independently in various embodiments of the present disclosure, or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

Various aspects and examples of an aircraft modal suppression system, as well as related methods, are described below and illustrated in the associated drawings. Unless otherwise specified, an aircraft modal suppression system in accordance with the present teachings, and/or its various components, may contain at least one of the structures, components, functionalities, and/or variations described, illustrated, and/or incorporated herein. Furthermore, unless specifically excluded, the process steps, structures, components, functionalities, and/or variations described, illustrated, and/or incorporated herein in connection with the present teachings may be included in other similar devices and methods, including being interchangeable between disclosed embodiments. The following description of various examples is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. Additionally, the advantages provided by the examples and embodiments described below are illustrative in nature and not all examples and embodiments provide the same advantages or the same degree of advantages.

This Detailed Description includes the following sections, which follow immediately below: (1) Definitions; (2) Overview; (3) Examples, Components, and Alternatives; (4) Advantages, Features, and Benefits; and (5) Conclusion. The Examples, Components, and Alternatives section is further divided into subsections, each of which is labeled accordingly.

The following definitions apply herein, unless otherwise indicated.

“Comprising,” “including,” and “having” (and conjugations thereof) are used interchangeably to mean including but not necessarily limited to, and are open-ended terms not intended to exclude additional, unrecited elements or method steps.

Terms such as “first,” “second,” and “third” are used to distinguish or identify various members of a group, or the like, and are not intended to show serial or numerical limitation.

“AKA” means “also known as,” and may be used to indicate an alternative or corresponding term for a given element or elements.

The terms “inboard,” “outboard,” “forward,” “aft,” and the like are intended to be understood in the context of a host vehicle on which systems described herein may be mounted or otherwise attached. For example, “outboard” may indicate a relative position that is laterally farther from the centerline of the vehicle, or a direction that is away from the vehicle centerline. Conversely, “inboard” may indicate a direction toward the centerline, or a relative position that is closer to the centerline. Similarly, “forward” means toward the front portion of the vehicle, and “aft” means toward the rear of the vehicle. In the absence of a host vehicle, the same directional terms may be used as if the vehicle were present. For example, even when viewed in isolation, a device may have a “forward” edge, based on the fact that the device would be installed with the edge in question facing in the direction of the front portion of the host vehicle.

“Processing logic” describes any suitable device(s) or hardware configured to process data by performing one or more logical and/or arithmetic operations (e.g., executing coded instructions). For example, processing logic may include one or more processors (e.g., central processing units (CPUs) and/or graphics processing units (GPUs)), microprocessors, clusters of processing cores, FPGAs (field-programmable gate arrays), artificial intelligence (AI) accelerators, digital signal processors (DSPs), and/or any other suitable combination of logic hardware.

A “controller” or “electronic controller” includes processing logic programmed with instructions to carry out a controlling function with respect to a control element. For example, an electronic controller may be configured to receive an input signal, compare the input signal to a selected control value or setpoint value, and determine an output signal to a control element (e.g., a motor or actuator) to provide corrective action based on the comparison. In another example, an electronic controller may be configured to interface between a host device (e.g., a desktop computer, a mainframe, etc.) and a peripheral device (e.g., a memory device, an input/output device, etc.) to control and/or monitor input and output signals to and from the peripheral device.

Directional terms such as “up,” “down,” “vertical,” “horizontal,” and the like should be understood in the context of the particular object in question. For example, an object may be oriented around defined X, Y, and Z axes. In those examples, the X-Y plane will define horizontal, with up being defined as the positive Z direction and down being defined as the negative Z direction.

“Providing,” in the context of a method, may include receiving, obtaining, purchasing, manufacturing, generating, processing, preprocessing, and/or the like, such that the object or material provided is in a state and configuration for other steps to be carried out.

In this disclosure, one or more publications, patents, and/or patent applications may be incorporated by reference. However, such material is only incorporated to the extent that no conflict exists between the incorporated material and the statements and drawings set forth herein. In the event of any such conflict, including any conflict in terminology, the present disclosure is controlling.

Overview

In general, a method of aircraft modal suppression and a corresponding system is described. The method and system of aircraft modal suppression encompasses a model-based design of a modal suppression control law. The underlying model utilized in determining the control law utilizes non-uniform gusts to accurately model the gust penetration of the aircraft in order to model the dynamics of the airframe when subject to turbulence. While previously known modeling techniques assumed that vertical gusts affected both wings symmetrically (referred to as “uniform models”), this limitation fails to accurately represent what is observed in testing and in nature, namely, that vertical gusts excite lateral vibration modes.

To solve this deficiency, a novel approach incorporating a “non-uniform” model was developed. The non-uniform model is configured to model the effect of turbulence by segmenting the airframe into multiple span-wise gust segments in a finite element model. The multiple segments effectively divide up the finite element model, thereby analyzing respective gust penetrations of each of the different span-wise locations of the model. The segments can then be combined into an accurate gust response, for example by computing the Von Karman cross spectra between the segments. The non-uniform model provides insight into the vibration modes that are excited in turbulence and the relative contribution of each mode to the response at a point on the aircraft. Accordingly, this information may be used to the optimize the design of the modal suppression control law.

The design of a feedback control law for an aircraft modal suppression system necessitates a tradeoff between performance and stability. In this context, performance is measured by the reduction of the unwanted vibrational modes stirred up in turbulence, with more reduction being desirable. Stability determines the ability of the system to operate without producing unwanted oscillations arising from an interaction between the control system and the response that it produces in the aircraft. In practice, the requirement for stability places a bound on the attainable performance of the aircraft modal suppression system.

For an aircraft with the familiar tube-and-wing design, lateral vibration is usually dominated by a symmetric, elastic deformation of the fuselage about its center, known as the first body bending mode. Reduction of lateral vibration due to first body bending can be accomplished by moving a control surface, for example a rudder, in opposition to the measured vibration from a sensor. If the aircraft response to the control surface movement is out of phase with the unwanted vibration, the lateral vibration is reduced.

In theory, an aircraft modal suppression system is usually most effective when the sensor and control surface are placed at the same location in or on the aircraft. In control engineering, this concept is known as collocated control. However, in practice, collocated control is not always feasible or even desirable for reasons of weight, cost, complexity, and/or challenges of spatial integration. Furthermore, the placement of sensors and control surfaces on the aircraft are often determined by other considerations such as the stability and control of the aircraft and the control system used to augment those characteristics. For this reason, the sensors and control surfaces available for the implementation of an aircraft modal suppression system may be sub-optimal for that purpose. Not using collocated control introduces challenges of observability and controllability. In the context of aircraft modal suppression systems, observability refers to the ability of the sensors to measure the unwanted vibration that the system seeks to reduce, while controllability refers to the ability of the control surfaces to effect a reduction in the unwanted vibration.

The problem of observability can be mitigated through the intentional design of a state observer, referred to subsequently simply as an “observer.” The purpose of the observer is to estimate one or more states of the aircraft by applying mathematical operations to data, e.g., from available sensor measurements. These estimated states may be physical in nature and represent quantities such as a position, velocity, or acceleration pertaining to a portion of the aircraft. One of ordinary skill in the art also recognizes the possibility that one or more of the estimated states may also be abstract in the sense that they correlate with a quantity of interest, such as the vibration of a specific portion of the aircraft, yet not represent it in a way that can be directly compared to the measurement of any hypothetical sensor located at that portion of the aircraft. Accordingly, the observer is useful to the design of an aircraft modal suppression system by estimating information that is otherwise unavailable by measurement. This information is consumed by the control law which will be described later.

For an aircraft with a single dominant elastic mode of vibration, the design of the aircraft modal suppression system is relatively simple, because the performance is summarized by the percentage reduction of the single dominant mode, leading to obvious design tradeoffs between performance and stability. However, as the design of airplane fuselages and wings become longer and more flexible due to competitive demands, additional modes of vibration may arise and complicate the aircraft modal suppression system design. Like the first body bending mode, the motion from these additional vibrational modes is unwanted and is detrimental to the aircraft's ride quality in turbulence. These additional vibrational modes also have different mode shapes, or a specific pattern of elastic deformation across the aircraft. To reduce the effects of the additional vibrational modes on the aircraft may necessitate the use of different control surfaces, such as ailerons and flaperons. When other modes are present there is also a risk of spillage, which is an undesirable amplification of modes that are adjacent in frequency to the modes that the aircraft modal suppression system is trying to reduce.

Furthermore, the performance of an aircraft modal suppression system becomes more difficult to evaluate when multiple significant vibrational modes exist. For example, suppose there are three modes and the control law designer has a choice between reducing only the first mode by 75% (with neutral impact to the other two modes), or equally reducing all three modes by 30% each. Without further information, it may not be readily apparent which of these two control law designs would result in a better ride quality.

The presently disclosed methods of aircraft modal suppression resolve this conundrum through an innovative use of the non-uniform model. Using the accurate gust response from this model, the control law designer determines the relative contribution of each vibrational mode to the aircraft response in turbulence. With this information the optimum control law can be identified and selected. Continuing the previous example, if the non-uniform model predicts that all modes contribute equally to the airplane motion in turbulence, then the second control law reducing each mode by 30% each is superior as it would result in a lower overall response of 2.1 (i.e., 0.7+0.7+0.7) compared to the first control law's response of 2.25 (i.e., 0.25+1+1). However, if the non-uniform model shows that the response is dominated by the first mode, then the other control law may be preferred.

Accordingly, in general, the disclosed methods of aircraft modal suppression include receiving a plurality of signals from on-board inertial sensors of an aircraft corresponding to motions of one or more portions of the aircraft. The on-board inertial sensors of the aircraft include sensors configured to measure accelerations, for example, at a forward portion, a midportion, and an aft portion of the fuselage of the aircraft. In some examples, the on-board inertial sensors are configured to measure lateral accelerations at the forward portion, midportion, and aft portion of the fuselage, as well as a yaw rate and a roll rate at the midportion of the fuselage. More generally, methods according to the present teachings may use inertial sensors at various locations on an aircraft.

The methods further include utilizing the plurality of signals to generate a plurality of observers. In some examples, generating the plurality of observers includes applying one or more operations such as addition, subtraction, and/or filtering to one or more signals of the plurality of signals. Each resulting observer comprises one or more estimated states of the aircraft, such as (for example) an estimated motion and/or acceleration of a portion of the aircraft, or an abstract state of the aircraft that is correlated to a quantity of interest, such as a degree of vibration of a portion of the aircraft. In some examples, each observer comprises one or more estimated states of a respective control surface of the aircraft, such as an estimated motion and/or acceleration of the control surface. For example, the plurality of observers may comprise estimated motions and/or accelerations at a rudder of the aircraft, at one or more ailerons of the aircraft, and/or at one or more flaperons of the aircraft. In other words, the measured signals of the on-board inertial sensors located at the forward portion, midportion, and aft portion of the fuselage may be utilized to generate observer estimations of motion/acceleration at control surfaces of the aircraft.

The estimated states (i.e., the observers) may then be utilized to determine control law commands for one or more control surfaces of the aircraft, such that vibrations of the aircraft are reduced. In particular, the control law commands are configured to reduce vibrations of the aircraft that are induced by a combination of uniform lateral wind gusts and non-uniform vertical wind gusts, although in some cases the lateral wind gusts might also be non-uniform. In some examples, the control law commands are configured to dampen lateral mode excitations of the aircraft. In some examples, the control law commands are configured to dampen lateral mode excitations having elastic contributions comprising frequency components below 10 Hertz. In some examples, the control law commands include antisymmetric commands for the ailerons and/or the flaperons of the aircraft.

As described herein, the modal suppression methods and systems utilize a Multi Input Multi Output (MIMO) feedback control law. This type of control strategy uses multiple sensors (inputs) and multiple control surfaces (outputs). In general, the methods utilize a plurality of on-board inertial measurement signals to construct a plurality of estimated observations of how a gust has excited an aircraft. The observations or estimates are referred to as one or more observers. The output of the observer(s) is used, e.g., as the input to high order shaping filters, to construct control law commands for one or more control surfaces of the aircraft.

Accordingly, the modal suppression methods and systems described herein are MIMO observer-based feedback controls configured to reduce the lateral vibration of the airplane based on a dynamic flight model that captures the effects of non-uniform gusts on the airframe. One of ordinary skill in the art will also recognize the possibility of using a feedback control law that is Single Input Single Output (SISO), Single Input Multiple Output (SIMO), or Multiple Input Single Output (MISO). Depending on the particular aircraft and the design constraints, one of these other feedback approaches may be selected instead.

The presently disclosed methods further include controlling (e.g., moving) the control surfaces in accordance with the control law commands. For example, the methods may include controlling the rudder, flaperons, and/or ailerons in accordance with the control law commands to reduce vibrations of the aircraft.

In actual implementation, there may not be a distinct separation between the part of the system creating the observations and the part of the system implementing the modal suppression control law. In some embodiments of the disclosed invention, some or all of the calculations needed to produce the estimated observations may be subsumed into the high order shaping filters also containing the control law. Aspects of the modal suppression systems and methods may be embodied as a computer method, computer system, or computer program product. Accordingly, aspects of the modal suppression systems and methods may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, and the like), or an embodiment combining software and hardware aspects, all of which may generally be referred to herein as a “circuit,” “module,” or “system.” Furthermore, aspects of the modal suppression systems and methods may take the form of a computer program product embodied in a computer-readable medium (or media) having computer-readable program code/instructions embodied thereon.

Any combination of computer-readable media may be utilized. Computer-readable media can be a computer-readable signal medium and/or a computer-readable storage medium. A computer-readable storage medium may include an electronic, magnetic, optical, electromagnetic, infrared, and/or semiconductor system, apparatus, or device, or any suitable combination of these. More specific examples of a computer-readable storage medium may include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, and/or any suitable combination of these and/or the like. In the context of this disclosure, a computer-readable storage medium may include any suitable non-transitory, tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device.

A computer-readable signal medium may include a propagated data signal with computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, and/or any suitable combination thereof. A computer-readable signal medium may include any computer-readable medium that is not a computer-readable storage medium and that is capable of communicating, propagating, or transporting a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer-readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, and/or the like, and/or any suitable combination of these.